Circuit arrangement for supplying eht to the accelerator anode of a picture display tube

ABSTRACT

A circuit has a horizontal output transformer with an output winding. A voltage multiplier is connected to the winding to provide the voltage to a CRT ultor electrode. In addition, a diode has its cathode connected to the junction of the multiplier and the winding and its anode grounded. This supplies the voltages for the acceleration anodes without using a large capacitor in the multiplier and reduces the current drain from the winding.

O United States Patent [151 3,702,414

Janssen 1 Nov. 7, 1972 [54] CIRCUIT ARRANGEMENT FOR 3,143,686 8/1964 Vonderschmitt et SUPPLYING EHT TO THE al. ..315/27 XY ACCELERATOR ANODE OF A 3,417,347 12/1968 Claverie ..315/29 X PICTURE DISPLAY TUBE 3,020,484 2/1962 Janssen et al. ..315/29 X [72] Inventor: Peter Johannes Hubert Janssen, 3,609,446 9/1971 Hursh et al. ..315/29 X iimnasingel, Eindhoven, Nether- FOREIGN PATENTS 0R APPLICATIONS an S 1,026,932 4/1966 Great Britain ..315/29 [7 3] Assignee: U.S. Philips Corporation, New

York Primary Examiner-Carl D. 'Quarforth [22] Filed: July 15, 1971 Assistant Examiner-P. A. Nelson Attorney-Frank R. Trifari [21] Appl. No.: 163,013

[57] ABSTRACT C(i1. ..315/29, A circuit has a horizontal output transformer with an [.1 p A voltage multiplier is connected to [58] Fleld of Search ..315/14, 27 R, 27 XY, 28, 29 the winding to provide the voltage to a CRT ultor electrode. In addition, a diode has its cathode con- [5 6] References cued nected to the junction of the multiplier and the wind- UNTTED STATES PATENTS ing and its anode grounded. This supplies the voltages for the acceleration anodes without using a large 2,801,364 7/1957 Janssen ..315/29 X capacitor in the multiplier and reduces the Current 2,801,366 7/1957 Janssen et al. ..315/29 X drain from the winding 2,879,447 3/1959 Preisig ..315/29 X 3,139,538 6/1964 Geller ..315/29 X 5 Claims, 2 Drawing Figures AIR A16 A18 PATENTEDnnv 1 m2 3.702.414

l L 13": if m 10 18 12 F|g.2

IXVEXTOR.

PETER JOIIANNES H. JAYFSYX CIRCUIT ARRANGEMENT FOR SUPPLYING EIIT TO THE ACCELERATOR ANODE OF A PICTURE DISPLAY TUBE The invention relates to a circuit arrangement for supplying EI-lT to the acceleration anode of a picture display tube in a picture display apparatus, comprising a line output transformer, an El-IT winding wound on the core of the transformer, a multiplier circuit constituted by capacitors and rectifiers, which multiplier circuit is connected to a terminal of the EI-IT winding, a diode and a parallel arrangement of a resistor and a capacitor being connected to terminals of the EHT winding.

Such a circuit arrangement is known from US. Pat. application, Ser. No. 231,764 and is shown in FIG. 1. In thisFIG. a load circuit consisting of the parallel circuit 1 in series with a diode 2 is arranged between the terminals of the EHT winding 3 in order that a small internal resistance of the EHT source is obtained. A positive voltage is produced at the junction of the parallel arrangement and the diode, which positive voltage is smoothed by a smoothing network 4, 5 so as to be applied to an acceleration anode A, of the picture display tube. A further step described in the said application is the use in the parallel circuit 1 of a capacitor having a much larger capacitance than that of the first capacitor 6 in the multiplier circuit 7. As a result the line output stage is safeguarded in case of flashover. v

A drawback of this known circuit arrangement is the following. Since it must be possible to adjust the supply voltage at the mentioned acceleration anode A a potentiometer, or three potentiometers when the picture tube is a color picture tube, must be arranged in parallel with the capacitor 5 of the smoothing network with the wipers of said potentiometers being connected to the anodes. This means that a current flows through the resistor 4 of the smoothing network, which causes a considerable and needless loss of power. A further drawback is the mentioned large capacitance of the capacitor in network I. Since this capacitor is to stand a high voltage, it must have large dimensions and it is expensive. An object of the present invention is to obviate these drawbacks and to render the safeguard in case of flash-over more effective and to this end the circuit arrangement according to the invention is characterized in that the cathode of the diode is connected to the junction of the EHT winding and the multiplier circuit, while its anode is connected to earth.

An embodiment of the circuit arrangement according to the invention is shown in FIG. 2 and will be described in greater detail hereinafter.

In FIG. 2 the cathode of the diode 2 is connected to the junction of the EHT winding 3 of the line output transformer and the multiplier circuit 7, while its anode is connected to earth. A capacitor 8 and three potentiometers 9, 10 and 11 are interconnected in parallel and in series with the winding 3. A resistor 12 having a relatively small resistance is arranged between the mary colors red, reen and blue reapectively. Since the voltage across po entrometers 9, l and 11 is high and since the anodes A A and A draw substantially no current, the potentiometers may be given high resistances so that the capacitance of capacitor 8 need not be large in order that the voltage at the anodes is satisfactorily smoothed, while the smoothing network 4,5 is not necessary, which may be considered as advantages of the circuit arrangement'according to the invention.

A beam current-dependent voltage which may be applied in known manner to a beam current limiter circuit is produced across the resistor 12.

When a flashover occurs in the picture display tube, the EHT lead, that is to say, the capacitor 13 in FIG. 2, is short-circuited to earth. As a result the charge of the capacitors in the multiplier circuit 7 is depleted through the diodes and a negatively directed current pulse is produced at the input of the circuit 7. The diode 2 then becomes conducting so that the said current pulse directly flows to earth without damaging the winding 3 or other non-shown parts of the line output stage present on the primary side of the transformer in which the winding 3 constitutes a secondary winding.

It is to be noted that it is advantageous to incorporate the diode 2 with the diodes and the capacitors of the multiplier circuit in one housing. It will be evident that the potentiometers 9, l0 and 11 may be replaced by a resistor of fixed value. The acceleration anodes are then connected directly or through an optionally variable resistor to the junction of the winding 3 and this re sistor of fixed value.

What is claimed is:

l. A circuit comprising a line output transformer having a high voltage winding, a voltage multiplier means coupled to a first end of said winding, means for supplying a voltage comprising a parallel circuit com prising a resistor and a capacitor coupled to an end of said winding, and means for preventing damage due to arcing comprising a diode having a cathode coupled to said first end of said winding and an anode coupled to ground for at least alternating currents.

2. A circuit as claimed in claim I wherein said parallel circuit is coupled to a second winding end.

3. A circuit as claimed in claim 1 wherein said resistor comprises a potentiometer.

4. A circuit as claimed in claim 1 wherein said supplied voltage is derived from said resistor.

5. A circuit as claimed in claim 1 wherein said anode is directly connected to ground. 

1. A circuit comprising a line output transformer having a high voltage winding, a voltage multiplier means coupled to a first end of said winding, means for supplying a voltage comprising a parallel circuit comprising a resistor and a capacitor coupled to an end of said winding, and means for preventing damage due to arcing comprising a diode having a cathode coupled to said first end of said winding and an anode coupled to ground for at least alternating currents.
 2. A circuit as claimed in claim 1 wherein said parallel circuit is coupled to a second winding end.
 3. A circuit as claimed in claim 1 wherein said resistor comprises a potentiometer.
 4. A circuit as claimed in claim 1 wherein said supplied voltage is derived from said resistor.
 5. A circuit as claimed in claim 1 wherein said anode is directly connected to ground. 